It is known that the pressure of the primary circuit of pressurized water nuclear power stations can be controlled in part, by submersible heating elements ("heating rods") disposed in the bottom part of the pressurizer, which usually takes the shape of a steel basin through the end of which vertical heating elements extend. For this purpose the end comprises a series of vertical tubular sleeves in which the heating elements can engage.
The technological difficulty of the problem is due to the fact that the pressurizer enclosure on which the submersible heating elements must be mounted via the agency of the sleeves operates at high pressures (of the order of 170 bar) and at elevated temperatures (which can go up to 350.degree. C.).
In the first pressurized water nuclear power stations set up in France, the metal submersible heating elements were welded to the sleeves, and this method was satisfactory as regards sealing-tightness and durability. However, such a method clearly has disadvantages in operation: it is a lengthy and expensive matter to remove a heating element, either for inspection or replacement, since the existing weld must be destroyed (possibly damaging the sleeve) and a new weld must be made. It will also be noted that the time during which action is taken cannot be prolonged indefinitely without serious disadvantages, since the pressurizer is `hot` and operatives carrying out the work are therefore subjected to irradiation. Moreover, such work (destroying the weld and then rewelding) requires a fresh hydraulic test under the regulations in force, since the integrity of the pressurized envelope has been `modified` by the welding.
In these conditions it seemed infinitely desirable to be able to install and remove the submersible heating elements in the sleeves quickly and without adverse effect on the sealing-tightness of the assembly, the integrity of the sleeve being ensured throughout.
There are numerous removable connecting assemblies which solve the problem of sealingly mounting a tube in a sleeve. More particularly screwed connections are known whose tightening compresses a joint.
In this respect the tests carried out by the Applicants with connecting assemblies of this kind proved to be ineffective, since due to the pressures involved, very high tightening torques are required, which may twist the sleeve.
It is an object of the invention to provide a connecting device which can be quickly installed and removed, and, above all provides an effective seal even at very high temperatures and pressures.
It is a further object of the invention to provide a method of installing and removing the said connecting device in such a manner that negligible torque is transmitted to the sleeve.
It is a further object to provide a prestressing jack for use with the connecting device of the invention.